1. Field
The present disclosure relates to methods for manufacturing a thin film transistor (TFT) and an array TFT, and more particularly, to methods for manufacturing a TFT and an array TFT by using a hybrid inkjet printing apparatus capable of ejecting a fine droplet.
2. Description of the Related Art
Thin film transistors (TFTs) are used in a variety of applied fields, in particular, in a display field as a switching and driving device. Photolithography has been established as technology for manufacturing the TFT. The photolithography is limited in using a functional material having conductivity and semiconductivity due to a deposition process. Also, when the photolithography is applied to a flexible substrate, misalignment may be generated due to a high deposition temperature so that process accuracy may be deteriorated and process costs may be high. To address the above issues, printing technology is employed gradually and increasingly as a replacement technology for the photolithography.
Many methods have been developed and applied for the printing technology. Among the many methods, an inkjet technology having a substrate non-contacting characteristic is evaluated as one of major innovative technologies. Accordingly, a lot of research activities have been performed globally due to its importance and usability.
A contact type printing is widely known as a method for implementing a TFT by printing. According to the contact type printing, when a new layer is formed on an already formed underlayer, liquid is printed by contacting the underlayer so that mechanical deformation or contamination may be easily generated in the substrate or underlayer. Also, if roughness of a printed surface is high or a printing area is large, printing is difficult because the printing area is determined according to the size of a mold.
Thus, a non-contact type inkjet printing technology is used to overcome the demerit of the contact type printing method. The non-contact type inkjet printing technology may form a variety of patterns by using a single printing apparatus and may prevent contamination between layers. An inkjet printing apparatus used for the non-contact type inkjet printing technology prints a predetermined image by ejecting a fine ink droplet at a desired position on a print medium.
The inkjet printing apparatus includes a piezoelectric inkjet printing apparatus for ejecting ink by using the deformation of a piezoelectric material and an electrostatic inkjet printing apparatus for ejecting ink by an electrostatic force, according to the type of ejection. The electrostatic inkjet printing apparatus includes a type of ejecting an ink droplet by electrostatic induction and a type of ejecting an ink droplet by accumulating charged pigments by an electrostatic force.
The piezoelectric inkjet printing apparatus has a difficulty in implementing an ultrafine droplet having a size smaller than several picoliters. Also, this printing apparatus has a problem in that an ink droplet does not accurately arrive at a desired position compared to the electrostatic inkjet printing apparatus. The electrostatic inkjet printing apparatus may implement an ultrafine droplet, employ a simple driving method, and exhibit superior directivity of an ejected ink droplet, which is suitable for precision printing. However, the electrostatic inkjet printing apparatus employing an electrostatic induction method have a demerit in that individual ink paths are difficult to form so that it may be difficult to eject ink from a plurality of nozzles by a drop-on-demand (DOD) method.
Thus, since precision printing of electrode and semiconductor liquid materials is made possible by employing a hybrid type inkjet printing technology having merits of both applied printing mechanism with apparatus, the printing is not affected by the type of substrate and printing technologies for forming a variety of patterns may be employed.